The need for renewable energy sources includes the need to improve the fuel burned by jet engines. It would be advantageous to have a high-volume continuous-flow manufacturing process appropriate to the high-volume needs of this market, which could produce material within the boiling range of jet fuel. As is known to those skilled in the art, utilizing a water-washing process produces emulsions that are time-consuming and troublesome to break. The residual water itself must be removed to minimize not only corrosion and growth of harmful organisms, but to eliminate the possible formation of ice crystals in chilled fuel, it is desirable to manufacture such fuel without any process contact whatsoever with water.
According to statements in U.S. Pat. No. 6,015,440 to Noureddini, biodiesel was used as a fuel in South Africa before World War II. Although oils such as peanut oil could be used as diesel fuel, it can be assumed that at least some of the diesel fuel was made using transesterification of glycerides, which art goes back to the early days of soap-making. The transesterification of glycerides has been the subject of many patents. Early patents such as U.S. Pat. Nos. 2,271,619 and 2,360,844 to Bradshaw, et al., U.S. Pat. Nos. 2,383,580 and 2,383,581 to Arrowsmith, et al., Re22751 to Trent, U.S. Pat. No. 2,383,614 to Percy, U.S. Pat. No. 2,494,366 to Sprules, et al. and U.S. Pat. No. 4,371,470 to Matsukura were concerned with making esters as a means of making pure fatty acids for making soap. Other early patents such as U.S. Pat. No. 2,290,609 to Goss, et al., U.S. Pat. No. 2,634,279 to Kuhrt, U.S. Pat. No. 2,875,221 to Birnbaum and U.S. Pat. No. 3,083,216 to Alsop, et al. were concerned with making mono and diesters of glycerin.
There have been many processes developed for making biodiesel from glycerides. This disclosure will focus on those processes using a basic catalyst. It will also focus on continuous processes, although batch-reaction, batch-separation, batch-washing and batch-polishing processes may be incorporated into an otherwise continuous process, or large reservoirs may be continuously fed and drained, and the whole process called “continuous,” as the biodiesel art is practiced. Strictly speaking, a continuous process has a continuous-flow everywhere, whether laminar or turbulent. It may be likened to a pipeline carrying a flowing liquid. A typical continuous process might be that described by Noureddini in U.S. Pat. No. 6,174,501. Triglyceride, methanol and catalyst are fed into a heated, stirred reactor. The upper layer is then fed into a separator. The upper layer is then passed through a deionization (“polishing”) unit to become biodiesel product. This disclosure, however, takes a portion of mono and diglycerides for the purpose of making lower alkyl ethers of the mono and diglycerides and the glycerin itself. Thus, it does not seek completeness of reaction or purity of ester product for it teaches reduction of cloud point by the production of what might be described as a racemic mixture, or a rafinate including ethers.
Many patents have been issued for the form of the reactor in which the chemical reaction takes place. The triglyceride and methanol are not seen to be miscible beyond a limited degree of solubility, and patents such as Boocock in U.S. Pat. No. 6,624,399 teach the addition of co-solvents such as cyclic ethers to give a homogenous solution. Several patents suggest reactors with enhanced stirring. Assmann, et al. in U.S. Pat. No. 5,514,820 teaches having a Reynolds Number in excess of 2,300. Hooker in U.S. Patent Application Number 2005/0027137 teaches ultrasonics to facilitate the reaction.
There is a large amount of art dealing with handling of the products of such a reaction. It is concerned with gross separation of reaction byproducts and fine separation of small amounts of unwanted material, and is done by chemical means, physical means or a combination.
The fatty acid alkyl ester is lighter than the glycerin phase (unless a very large alcohol excess is used, e.g. 20:1), and will separate by gravity. Wimmner in U.S. Pat. No. 5,399,731 claimed that the addition of 0.3% to 3.0% water would facilitate the separation. In contrast, McDonald in U.S. Pat. No. 6,262,285 claims without examples that by eliminating all water and using a continuous decantation that the separation can be done very effectively. McDonald removes all water with Molecular Sieves, one type of sorbent. There is no evidence presented that the procedure is effective as claimed.
The use of a centrifuge to separate two phases of differing density is, of course, very old technology as demonstrated by the cream separators of the 1800s. Many patents mention, in passing, that a centrifuge could be employed in biodiesel production. For example, see Assmann in U.S. Pat. No. 5,514,820 col. 2 line 7 and line 13, Granberg, et al. in U.S. Pat. No. 5,648,483 col. 7 line 51, Matsukura, et al. in U.S. Pat. No. 4,371,470 col. 3 line 18 and in U.S. Pat. No. 4,668,439 col. 6 line 25, Hayafuji, et al. in U.S. Pat. No. 5,972,057 col. 15 line 38 and Noureddini in U.S. Pat. No. 6,174,501 col. 10 line 59. In Barnhorst, et al. U.S. Pat. No. 6,489,496, the essential claim was for the use of a centrifuge.
McDonald in U.S. Pat. No. 6,262,285 claimed that separation by decantation gave an acceptable product.
There is a consensus among those skilled in the art that traces of impurities can be very serious, in addition to not meeting current U.S. and European biodiesel standards. There are several ways of removing impurities, wherein the biodiesel is first water-washed and then dried. Three examples of water-washing are Tanaka, et al. in U.S. Pat. No. 4,303,590, Boocock in U.S. Pat. No. 6,624,399 and Felly in U.S. Patent Application Number 2006/0224005. Connemann, et al. in U.S. Pat. No. 5,354,878 proposes the use of an aqueous pH 8 to 10 buffer to wash the biodiesel. In contrast, Wimner in U.S. Pat. No. 5,434,279 washes with dilute acid such as citric acid. Bam, et al. in U.S. Pat. No. 5,424,467 proposes the washing to be with glycerin. Hayafuji in U.S. Pat. No. 5,972,057 proposes the use of a sorbent such as acid clay. Bertram, et al. in U.S. Patent Application Number 2005/0081536 proposes the use of adsorbent such as magnesium silicate. Noureddini in U.S. Pat. No. 6,174,501 uses an ion-exchange resin to remove the impurities.